But now Secret’s founders want to push the service into the mainstream with new features intended to broaden the potential audience of the app.

On Monday, the company will release a new version of the application that will allow people to sign up for Secret and find friends using their Facebook credentials. Previously, the service relied on a user’s address book and list of contacts to find friends and see their Secret posts.

Linking Facebook to a service that is largely anonymous seems counterintuitive. But David Byttow, co-founder and chief executive of Secret, said such linking was the most requested feature from Secret users, who are eager to see more content posted through the service.

“I definitely feel like early adopters might balk at it a bit, but in mainstream people just want more conversation,” he said in a recent interview.

Mr. Byttow said that connecting by using Facebook would be entirely optional.

In addition, the company is introducing “collections” that will help organize messages posted on Secret and make it easier to browse by topics, such as humor, dating or food.

“We want to show what kind of conversations” people are having on Secret, he said, “and see where that takes us.”

He also said that this new feature release was “just step one” and that he hoped the most popular Secrets would eventually be indexed on Google and show up in relevant search results.

“There’s so much good content and amazing conversations that people are having,” Mr. Byttow said. “It should live beyond Secret.”

To help with that mission, the company also announced on Monday that it raised an additional $25 million in venture financing from a number of esteemed firms and angel investors, including Index Ventures, Redpoint Ventures, SV Angel and Fuel Capital. Previously, it raised $10 million. The new funding puts the valuation of Secret, a six-month-old company, at higher than $100 million.

The new funding also puts Secret more squarely in competition with Whisper, a rival anonymous-sharing application. Whisper recently raised $39 million in venture financing and has long organized messages into categories and topics for their users to peruse.

Correction: July 14, 2014An earlier version of this post and its headline misstated the amount raised by Secret. It is $25 million, not $20 million.